For loading furniture into trucks, for example, there are several conventional procedures. Manual lifting from the ground is dangerous and tiring. Alternatively, a long ramp leading from ground level to the truck platform is used to permit loaded wheeled dollies to be rolled up the incline and onto the truck. That has the disadvantages of requiring manual moving of a heavy load from ground level to truck platform level and restriction of use to places that the long ramps can be positioned. Shorter and steeper ramps are more dangerous and require greater maximum manual force. Accordingly motorized lift platforms have been suggested for reducing the manual effort necessary to move loads between ground levels and the truck platforms. These motorized lift platforms however have not been entirely successful and have various deficiencies.
In general, lift platforms are expensive, difficult to install- often requiring extensive modifications to standard truck construction- and impose obstructions to truck design or accessibility, including those requiring more room and extending truck body length or height, or those introducing dangers in operation or in storage. Some explicit examples of prior art motorized lifts and hoists disclosed in U. S. Patents follow.
Lift platforms with hydraulic mechanisms require expensive and complicated mechanisms for moving loads both laterally and vertically and a source of hydraulic power, as evidenced by 3,233,758, J. M. Darfus, Feb. 8, 1966 for Lift Gate. Also the support of such elevating mechanisms require high superstructure extending far above the truck platform and appropriate truck construction for anchoring at both bottom and top ends. Nor are these sorts of elevators easy to store without interference or modification of equipment.
An electric motor is used with expensive worm drive and rack pinion assembly for vertical movement in 2,405,054, O. R. Pringle, Jul. 30, 1946 for Elevating End Gate. This requires a heavy motor that quickly drains the conventional truck battery and significant modification to usual truck framework.
The motorized winch system of 2,590,591, H. E. Winkler for Adjustable Tail Gate Lift Assembly, Mar. 25, 1952 also requires an expensive winch and motor drive mounted below the truck platform and a twin tower hoist mechanism mounted on the platform to interfere with loading space.
Because of difficulties in storing a lift elevator system on board the truck, 3,180,503, F. J. Shaw, Apr. 27, 1965 for Detachable Tail Gate Lift for a Truck discloses a non-motorized assembly that can be hooked onto a pivot rod added to the truck frame and supported against a bumper. The load platform alternatively can be pivoted when not in use into the truck body to replace a conventional tail gate. The load is elevated by means of two lift screws manually rotated by a wrench. Operation is slow and tedious, and the platform may become dislodged because it is not secured in place when handling loads.
This sort of prior art introduced other problems and deficiencies and fails to solve some urgent problems. For example, prior art devices are not suitable for use on flat body trucks, with or without side stakes. Furthermore the cost and inconvenience of custom installation and changes in body work or frame design is prohibitive. Nor has the prior art adequately dealt with problems of interfacing with the ground or equivalent support surfaces. Thus, unstable or tilted platform system ground contact in the presence of heavy loads is dangerous and intolerable. Another problem is the interfacing of loads initially on the platform. One example is that prior art elevator platforms are disposed so that loads such as heavy furniture, etc. may have to be manually transferred from a wheeled dolly to the load lift platform, and then manually moved or replaced on a wheeled dolly for placement in the moving van or on the truck bed.
It is therefore a general object of this invention to provide improved load lift systems and apparatus solving the aforesaid problems and deficiencies of the prior art.
Other objectives, features and advantages of the invention will be found throughout the following description, drawings and claims.